Max_message_size not taking effect

[imysl0]

When I try to send larger attachments (30.33MB), it always fails, but attachments of 13.66MB can be sent successfully. My settings allow for much more than 30.33MB, so why am I still encountering failures when sending the larger file?

imap: listening on tls://0.0.0.0:993	

imap: listening on tcp://0.0.0.0:143	

imapsql: loaded a large mailbox with 10110 messages, beware of performance issues	

submission: rDNS error	{"reason":"DNS response contained records which contain invalid names","src_ip":"192.168.1.3:48138"}

submission: incoming message	{"msg_id":"552598d7","sender":"xxxx","src_host":"[127.0.0.1]","src_ip":"192.168.1.3:48138","username":"xxxx"}

submission: RCPT ok	{"msg_id":"552598d7","rcpt":"xxxx"}

submission: DATA error	{"msg_id":"552598d7","reason":"I/O error while writing buffer: buffer: failed to write file: SMTP error 552: Maximum message size exceeded"}

submission: aborted	{"msg_id":"552598d7"}

[foxcpp]

Unable to reproduce the issue, however, another one exists - the returned error is not correct, SMTP client sees "Internal server error" instead of Maximum message size exceeded.

[imysl0]

Unable to reproduce the issue, however, another one exists - the returned error is not correct, SMTP client sees "Internal server error" instead of Maximum message size exceeded.

First of all, thank you very much for your reply. I'm quite confused. I set up a maddy server using Docker. When testing its account on a mobile email app, if I select an attachment, like a 30MB file, the app immediately warns that the file size is limited to 20.97MB, even before I send it. But when I use other regular email accounts (not self - hosted), there's no such warning. So, is this a configuration issue? Are there any possible causes to suspect?
my conf file：
maddy.txt